The present invention relates to container conveyor systems and, more particularly, a system that can be used, for example, to transport foundry moulds. State-of-the-art technique concerning such systems is very extensive, as is borne outxe2x80x94for examplexe2x80x94by U.S. Pat. No. 1,798,485.
The system described in the said document comprises a plurality of trolleys moving on rails laid out to form a loop consisting of two parallel straight lines that are joined by appropriately curved sections at both ends. The movement of the trolleys along the rails is obtained by means of a pushing unit that causes the trolleys to move forward in an intermittent manner.
Various factors have to be borne in mind when realizing systems of this kind. Some of these are bound up with the layout of the structure along which the trolleys are to be moved and the manner in which this movement is to be obtained.
In particular, the choice of employing a rail system laid out in the manner of a loop that has bends at the two ends is associated with the undoubted advantage provided by the fact that the trolleys can be moved along the rail like the carriages of a train: one need only think, for example, of the trolleys of a narrow-gauge railway of the type often used, for example, in mining installations. On the other hand, the presence of the two curved sections constitutes an intrinsic limitation as far as encumbrance is concerned, because the radius of curvature of the terminal bends cannot be reduced below minimum limits that depend on the size of the trolleys employed.
As far as trolley movement control is concerned, on the other hand, one solutionxe2x80x94in many ways idealxe2x80x94is to provide each trolley with its own motor means (an electric motor, for example). The principal advantage of this solution derives from the fact that the movement of each trolley can be controlled in a wholly independent manner. It is thus possible, for example, to arrange matters in such a way that one or more trolleys will be standing still in front of some processing station, to let the castings in the moulds pass through a cooling phase for example, while other trolleys will be on the move between successive processing stations. But this solution can prove very costly, especially in complex systems that involve a large number of trolleys, precisely because has to be provided with its own motor and control means, as also with means for supplying the necessary energy. Nor must one forget the fact that a working environment like the one constituted by foundries can prove very hostile for electric motors and the organs normally associated with them.
These critical factors suggest the realization of systems like the one used as model for the preamble of claim 1 hereinbelow. The system in question is a container conveyor system, especially for foundry applications, and has been produced for many years by the present applicants.
The guide structure of the said system is made up of two straight and parallel transport tracts, each of which accommodates a rectilinear line of containers devoid of motors of their own and moving forward on, for example, rollers or similar. At its two ends, moreover, the systemxe2x80x94which thus assumes the general configuration of a rectanglexe2x80x94also comprises appropriate transfer devices capable of transferring the containers from one straight line of non motorized trolleys to the other in accordance with a general container circulation pattern.
The movement of the containers that find themselves on the two rectilinear conveyor tracts is obtained thanks to the action of two pusher organs (which may be hydraulically operated, for example), each of which pushes its line of containers, which bear against each other without solution of continuity, moving them forward a step at a time, where the length of the step usually corresponds to the dimension of the individual container in the direction of motion. A complementary and structurally similar organ operates on the opposite end of each conveyor tract and has the task of realizing an action that will oppose the forward motion under the action of the pusher of the back-to-back container lines, but will do so in a yielding and controlled manner. At the two ends of each rectilinear conveyor tract there are usually arranged appropriate thrust-counteracting units intended to ensure that the step-by-step forward movement of the container lines will take place in a regular and controlled manner.
In actual practice, the pusher devices, of which there is one on each rectilinear conveyor tract, operate in a coordinated manner and in opposite directions, while the transverse transfer devices at the two ends of the system act likewise in a coordinated manner and in opposite directions, so that on each occasion they will pick up a single container at the output end of one rectilinear conveyor tract and transfer it to the immediately adjacent input end of the other container line. Taken as a whole, the described actions will thus realize a general circulatory movement of the containers along the conveyor structure of the system. A system of this kind can be used, for example, in a plant operated in accordance with what is currently known as  less than  less than lost-foam greater than  greater than  technology. Along the line of motion of the containers there will thus be arranged a series of processing stations, each designed to perform a specific operation on the said containers: placing the polystyrene models into the containers, filling the containers with sand, vibrating the sand in order to distribute and compact it evenly around the polystyrene models, pouring the casting material and, lastly, extracting the castings from the containers and removing the sand carried in the containers. The operations of filling and vibrating the sand are usually carried out in several successive steps.
An intrinsic drawback of the solution in accordance with the previously described known technique is constituted by the fact that during the performance of the operation or operations of vibrating the sand care has to be taken to ensure the vibratory motion applied to the container or containers in which the sand is being compacted will not be transmitted to any of the adjacent containers. As we saw in the previous description, the said containers are arranged back-to-back, so that the vibrated container would normally be in direct contact with another container on either side of it.
For this reason, the systems of this type so far produced by the present applicants always had to make provision for at least slightly separating these adjacent containers from the container that at any given time was being subjected to vibration.
On completion of the vibration operation and before the line of containers can resume its forward movement, the previously created distance to separate the adjacent containers must therefore be eliminated under the action of the pusher device, thus bringing the containers once more into their original back-to-back condition.
These operations can therefore give rise to undesired impact phenomena between adjacent containers and, more particularly, undesired displacements of the polystyrene models inserted into the said containers and not yet completely covered by sand.
Notwithstanding this problem, the system just described is associated with considerable advantages, especially as regards its simplicity and operational reliability.
The present invention therefore has the scope of realizing a system of the type specified hereinabove that will be devoid of the previously described negative phenomena, while yet preserving the aforesaid characteristics of simplicity and reliability.